The purpose of the proposed research is to understand the impact of environmental lighting on reproductive rhythms--both behavioral and physiological. There are several ways of approaching this problem: first of all, male behavioral rhythms, both circadian and infradian, have been detected. We would like to pursue this issue with documentation of the actual behavior, and by searching for the underlying physiological variables. We also would like to study the effects of photoperiod on male sexual behavior and the physiological bases for its effects. Secondly, we want to determine the etiology of the persistent estrus syndrome induced by exposure to constant light. This will be done, first of all, by measuring circadian and infradian estradiol rhythms using chronic cannulae to determine how these rhythms are altered. In addition, we will attempt to show if ovarian sensitivity is altered after exposure to constant light, thus contributing to the anovulatory state. In addition, we will assess the contribution of stress-induced adrenocortical secretions to the disruption of the estrous cycle in constant light. We will also examine phase-shifting of activity and receptivity rhythms, and measure, using telemetric signals, physiological variables such as heart rate and core temperature, as well as the basic endocrine landmarks of the cycle, to determine if this could account for disruption of the cycle in constant light. Thirdly, we will examine the major events of the estrous cycle in animals permitted to self-select their own lighting environments. Finally, we will investigate the role of the pineal in entrainment of hamster activity, receptivity and endocrine rhythms to alterations in photoperiod.